This project explores the largely unexplored concept of cholesterol interaction with proteins. Some indirect measures have suggested that such interactions may be important in the structure of human low density lipoprotein (LDL) and band 3 protein (anion transport protein) from the human erythrocyte membrane. Because of the roles of LDL and cholesterol in the pathogenesis of atherosclerosis, it is important to explore the behavior of cholesterol in two of its locations in human blood, low density lipoproteins and the erythrocyte membrane. Discovery of an interaction with protein would significantly alter the common view of cholesterol behavior in membranes and lipoproteins. This proposal probes by direct, non-perturbing methods (for the first time) and new indirect and somewhat perturbing methods the possible interaction of cholesterol with protein in: 1) LDL, and 2) the erythrocyte membrane. Two proteins from the erythrocyte membrane will be examined; MN-glycoprotein (glycophorin) and band 3 protein. 31P NMR, 2D NMR, ESR and CD measurements will be explored. The results will be employed to describe more fully the structure of LDL and the erythrocyte membrane, and lipid-protein interactions in these systems. The information should prove valuable to the understanding of the transport of cholesterol and the development of the placques of atherosclerosis.